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>Higher voltage is prolly the easiest to achieve -- just add another stage or three in the voltage multiplier. Overcurrent becomes a real danger for most experimental fusors b/c of the negative dynamic resistance characteristics of glow discharges.

One of the advantages of a multiplier supply is that it is effectively power limited.. If the resistance of the load drops (or flashes over), the output voltage drops dramatically, and in any case, if the filter caps are small enough, the discharge transient won't melt anything.